124 lines
3.6 KiB
Java
124 lines
3.6 KiB
Java
/*
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* The MIT License (MIT)
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*
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* Copyright © 2020 xrv <xrg@live.com>
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package io.github.ehlxr.algorithm;
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/**
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* @author ehlxr
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* @since 2021-12-28 23:16.
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*/
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public class FindKthLargest {
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public static void main(String[] args) {
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int[] nums = new int[]{3, 2, 1, 5, 6, 4};
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System.out.println(findKthLargest(nums, 2));
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}
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public static int findKthLargest2(int[] nums, int k) {
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for (int i = nums.length / 2 - 1; i >= 0; i--) {
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// 从第一个非叶子结点从下至上，从右至左调整结构
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adjustHeap(nums, i, nums.length);
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}
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for (int j = nums.length - 1; j >= 0; j--) {
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k--;
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if (k == 0) {
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return nums[0];
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}
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swap(nums, 0, j);
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adjustHeap(nums, 0, j);
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}
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return 0;
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}
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public static void adjustHeap(int[] arr, int i, int length) {
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// 先取出当前元素 i
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int temp = arr[i];
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// 从 i 结点的左子结点开始，也就是 2i+1 处开始
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for (int k = i * 2 + 1; k < length; k = k * 2 + 1) {
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// 如果左子结点小于右子结点，k 指向右子结点
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if (k + 1 < length && arr[k] < arr[k + 1]) {
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k++;
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}
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// 如果子节点大于父节点，将子节点和父节点交换
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// if (arr[k] > arr[i]) {
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// swap(arr, k, i);
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if (arr[k] > temp) {
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// 不用进行交换
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arr[i] = arr[k];
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i = k;
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} else {
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break;
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}
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}
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// 将 temp 值放到最终的位置
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arr[i] = temp;
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}
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public static int findKthLargest(int[] nums, int k) {
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if (nums == null || nums.length < k) {
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return -1;
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}
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int q = partition(nums, 0, nums.length - 1);
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while (q + 1 != k) {
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if (k < q + 1) {
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q = partition(nums, 0, q - 1);
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} else {
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q = partition(nums, q + 1, nums.length - 1);
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}
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}
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return nums[q];
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}
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public static int partition(int[] a, int p, int r) {
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int pivot = a[r];
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int i = p;
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for (int j = p; j < r; j++) {
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if (a[j] >= pivot) {
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swap(a, i++, j);
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}
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}
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swap(a, i, r);
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return i;
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}
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private static void swap(int[] a, int i, int j) {
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if (i == j) {
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return;
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}
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int temp = a[i];
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a[i] = a[j];
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a[j] = temp;
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}
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}
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